1. Field of the Invention
This invention relates to a constant velocity ratio plunging universal joint, comprising an inner joint member, an outer joint member, a plurality of balls engaging in facing pairs of tracks disposed circumferentially about the joint members for torque transmission therebetween, said tracks in each joint member having centre lines extending parallel to the axis of rotation of the joint member, and a cage of annular form between the joint members and holding the balls so that their centres lie in one plane. Such a joint will hereafter be referred to as a joint of the kind specified.
2. Description of Prior Art
In one well known embodiment of joint of the kind specified, the cage has a part-spherical internal surface and a part-spherical external surface, the centres of curvature of such surfaces being offset by equal distances on opposite sides of the plane in which the centres of the balls are held. The part-spherical external surface of the cage engages an internal cylindrical surface of the outer joint member between the tracks thereof, while the part-spherical internal surface of the cage engages a part-spherical surface provided on a sleeve which is slidable axially on a cylindrical surface of the inner joint member between the tracks thereof. Such a cage configuration has the effect of guiding the plane containing the centres of the balls so as to bisect the angle between the rotational axes of the inner and outer joint members when the joint is articulated, thereby ensuring that the joint has constant velocity ratio (homokinetic) running properties. The arrangement of the sleeve axially slidable on the inner joint member means that the cage is able to move axially relative to both joint members, thereby facilitating the plunging of the joint with minimal frictional resistance thereto.
It would be desirable if, when the joint plunges (i.e. the joint members move axially relative to one another), the cage moves by an equal distance relative to each of the joint members and when the joint members are in a position in the middle of their range of plunging movement relative to one another, the cage is centered in its range of movement relative to each joint member. In practice, however, depending on the frictional conditions between the cage and the two joint members, the cage will assume a position at the end of its range of movement relative to one or other of the joint members, even when the joint members themselves are in their central relative position. In consequence, when the joint plunges out of such position in one of the two possible directions, the cage will not be able to move further relative to one of the joint members, and the torque-transmitting balls will not be able to roll freely along the tracks in such joint member. Consequently there will be an undesirable high sliding frictional resistance to such plunge.
Plunging constant velocity ratio universal joints are also known from DE-PS-1251595, wherein the torque-transmitting balls engage in tracks whose centre lines lie in planes containing the rotational axes of the respective joint members. The centre lines are not parallel to such axes, however, and the tracks of each facing pair diverge from one another. Around the joint, the facing pairs of tracks diverge from one another alternately in opposite directions axially of the joint. This joint, however, has a disadvantage in that because of the necessary circumferential distance between the balls, the depth of part of the tracks receiving the balls decreases considerably in one axial direction, limiting the torque transmitting capacity of the joint. Further, the track shapes are difficult to produce.